Soil temps may cool
Corn planting started
Predicting corn emergence
Evaluating plant stands
Scout for Alfalfa Weevil

Introduction
Area soils should be filled to capacity with the recent precipitation events.  Check out precipitation totals at this web address:  http://www.hprcc.unl.edu/products/current.html.  Degree-day accumulation has been much above normal the past two weeks, but should level off to near normal for the next seven days.  Soil temperatures have followed the warm air temps the area has had, which has spurred corn planting across much of the area.  With potentially cooling soils and wet conditions, be sure to monitor emergence and stand quality.  Use the predicted emergence dates in Table 2 to evaluate when to begin looking.  Scouting for alfalfa weevil should begin in area fields as greater than 250 degree-days have been accumulated.

Weather information
Soil Temperature Area soil temperatures are running above normal and similar to a pattern observed over the last 3 years (see figure 1) with a “warm” peak observed over the previous few days then a rapid cool down over the next week.  Air temperatures are forecasted to be cooler, it will be interesting to see if soil temperatures follow and complete the pattern observed over the last three years.  Continue to monitor soil temperature at this web address:  http://mesonet.agron.iastate.edu/agclimate/display.php?src=/agclimate/daily_pics/4in-temp-out.png and the three day forecast at this URL: http://extension.agron.iastate.edu/NPKnowledge/Soiltemp/forecast.jpg

Growing Degree Day accumulation is shown in Table 1 and Figure 2 and is forecasted through April 26.  Degree day accumulation through April 19 has been much above normal (73 over the last 7 days vs. the normal of 33.  Similar to soil temperatures, in previous years the April 13 – 19 period has been warm and then has been followed by a much cooler week.  Looks like this year’s seven day forecast will be similar to 2003 but warmer than last year (table 1).  Even with the cooler week ahead, forecasted degree-days will be near normal.  Typically, corn will emerge with an accumulation of 110 to 140 degree-days (base 50).

Table 1.  Degree-Day Weekly Accumulation
	2005	2004	2003	14-Yr Ave
April 13 - 19	73	77	62	30
Forcasted April 20 - 26	33	19	31	33

Crop Management
Corn planting is underway in some areas and soybean planting will soon follow.  Even with the best soil conditions, emergence problems can occur.  Therefore; frequent field inspections should occur on a regular basis to monitor stand establishment and crop health.  If a stand problem is found, spend the time to determine what caused the reduced stand, whether it may be from seedling disease, uneven seed placement by the planter, rodents, or insect pests.  Make it a habit to pull plants and inspect roots.  The root system will tell a lot about plant health and general soil conditions (compaction, herbicide injury, disease, and insect feeding).  Early inspection of roots may help answer questions later in the season.  Use Tables 3 and 4 when inspecting plant populations and stand development.  For more detailed information on the basics of corn planting, see also the ISU Extension “Corn Planting Guide”

Table 3. Plant to Plant Spacing for Various Plant Populations
Inches between kernels or plants
Seed/A	20” row	30” row	38” row
24,000	13.1	8.7	6.9
26,000	12.1	8.0	6.3
28,000	11.2	7.5	5.9
30,000	10.5	7.0	5.5
32,000	9.8	6.5	5.2
34,000	9.2	6.2	4.9
36,000	8.7	5.8	4.6
38,000	8.3	5.5	4.3

 

Table 4. Length of row to equal 1/1000th acre
	Row Width	Length of row
	Inches	Feet	Inches
	20	26	2
	30	17	5
	38	13	9

Seed germination…what to look for.  Corn kernels must absorb about 30% of their weight in water before germination begins.  In comparison, soybeans must absorb 50% of their weight in water.  The three major events in the germination process in order include 1) the emergence of the radicle root (emerges as soon as 2 days after planting and up to 2-weeks in cold soils), 2) the plumule (eventually differentiates into the mesocotyl and coleoptile (spike)), 3) the lateral seminal roots emerge last.  Cool soils may delay the appearance of the coleoptile and seminal roots for more than a week after the radicle root emerges. 
 (Source:  The Germination Process in Corn, Nielsen, R.L.)

Predicted Corn Emergence Dates  Last year I used corn and soybean growth simulation models to predict crop emergence dates based on location and planting date.  I am running the models again this year and will post the results here.  This year I am using a different corn model (Hybrid Maize) developed by specialists at the University of NE, but I expect results to be as good or better than the previous model (DSSAT) that I used.  With warms soils and even warmer air temperatures, current emergence predictions have the corn up within six to nine days following planting.  If soils cool over the next couple of days and with the wet conditions, emergence may be delayed from the predictions.  If you have questions on how this data was developed, please give me a call.  The current forecast on corn emergence is found in Table 2. 

Table 2.  Predicted corn emergence dates by planting date and location
	County
Planting Date		Story	Monona	O'Brien	Hancock		Average
April 10		19-Apr	20-Apr	19-Apr	19-Apr		19-Apr
April 15		21-Apr	21-Apr	22-Apr	23-Apr		21-Apr
April 20
April 25
April 30
May 5
May 10

Pest Management
Alfalfa weevil: Weevil scouting in alfalfa should begin when accumulated degree-day (DD) counts reach 250.  Current degree-day count is at 322 for N.W. Iowa and reached the magical 250 around April 16.   More information on Alfalfa Weevil can be obtained from the April 11 issue of the ISU ICM newsletter, found at this URL:  http://www.ipm.iastate.edu/ipm/icm/2005/4-11-2005/scoutweevil.html

Black Cutworm Trap Catch  Keep current on black cutworm trap catches at this URL:
http://www.ent.iastate.edu/trap/blackcutworm/

Soybean Rust  Continue to monitor the USDA and North Carolina websites on the potential movement of rust and scouting occurring across the U.S.  Currently, only three counties in Florida have confirmed soybean rust.  More and more counties are showing up as being scouted, and fortunately are marked as “not found”.   The April 10 and 11 spore dispersal forecasts (http://www.ces.ncsu.edu/depts/pp/soybeanrust/forecasts/s050410.php) are two evens that could be important to watch.  Spores may have been moved into the lower Mississippi river valley which could open the door to movement into the upper Midwest. 

Tracking soybean rust: http://www.sbrusa.net/

Spore dispersal Forecast  http://www.ces.ncsu.edu/depts/pp/soybeanrust/index.php